The Dykstra-Parsons method is often used to study the displacement of oil by water or gas in stratified reservoirs. These strata of different permeability are assumed to exhibit lateral continuity throughout the reservoir. In the proposed model, these strata are assumed to consist of several blocks with differenl transmissibility, kh/μ, and storage, ϕcth. According to Dykstra and Parsons, the displacing fluid sweeps faster through the more permeable zones so that much of the oil in the less permeable layers must be produced over a long period of time at high WOR. In this study, it is found that this is not necessarily true. It simply depends on the rock characteristics from layer-to-layer and from block-to-block. It is also found that waterflooding performance in layered-composite reservoirs is essentially controlled by the mobility ratio.

Equations giving the pressure drop, time of breakthrough, water-front location, coverage, WOR and cumulative oil recovery in a layered-composite reservoir are presented. Application of these equations to the case of constant injection pressure, which was not treated by the original Dykstra-Parsons method, is discussed.

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